Liquid crystal device with at least two liquid crystal compounds, one having and one not having a chiral smectic phase

ABSTRACT

A liquid crystal device is constituted by (a) a pair of base plates each having an orientation control film thereon, and (b) a liquid crystal composition interposed between the base plates. The liquid crystal composition comprises a mixture including at least one liquid crystal compound which has a temperature range in which it shows chiral smectic phase and at least one optically active substance which does not have a temperature range in which it shows chiral smectic phase. The liquid crystal composition has a temperature range in which it shows cholesteric phase and is placed in chiral smectic phase which has been formed through cholesteric phase on temperature decrease. The liquid crystal composition comprises liquid crystal molecules having long axes forming a pre-tilt in the chiral smectic phase.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.863,781, filed Apr. 6, 1992, which in turn is a continuation-in-part ofapplication Ser. No. 251,028, filed Sep. 26, 1988, now issued as U.S.Pat. No. 5,120,466, which in turn is a continuation of application Ser.No. 750,295, filed Jul. 1, 1985, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal device for use in aliquid crystal display device, an optical shutter array, etc., and moreparticularly to a liquid crystal device having improved display anddriving characteristics, because of improved initial alignment ororientation of liquid crystal molecules.

Hitherto, there have been well known liquid crystal devices using TN(twisted nematic) type liquid crystal as shown, for example, in"Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal"by M. Schadt and W. Helfrich, Applied Physics Letters Vol. 18, No. 4(Feb. 15, 1971) pp. 127-128. In this type of liquid crystal device, thenumber of picture elements has been restricted, because there is aproblem that a crosstalk phenomenon occurs when a device of a matrixelectrode structure with a high density of picture elements is drivenaccording to a time-sharing or time-division driving scheme.

As another type of liquid crystal device, there has been known onecomprising a plurality of picture elements each connected to and subjectto switching by a thin film transistor as a switching element. This typeof liquid crystal device, however, is accompanied with problems suchthat production of thin film transistors on a substrate is verycomplicated, and production of a display device with a large picturearea or screen is difficult.

In order to obviate the above-mentioned draw-backs of the conventionaltypes of liquid crystal devices, Clark and Lagerwall have proposed theuse of a liquid crystal device using a bistable liquid crystal (JapaneseLaid-Open Patent Application No. 107216/1981, U.S. Pat. No. 4367924,etc.). The bistable liquid crystal to be used may be a ferroelectricliquid crystal having a chiral smectic C (SmC*) phase or another phasesuch as chiral smectic H (SmH*) phase, chiral smectic F (SmF*) phase,chiral smectic I (SmI*) phase or chiral smectic G (SmG*) phase.

Such a ferroelectric liquid crystal has bistability, i.e., has twostable states comprising a first stable state and a second stable state.Accordingly, different from the conventional TN-type liquid crystal inthe above-mentioned device, the liquid crystal is oriented to the firststable state in response to one electric field vector and to the secondstable state in response to the other electric field vector. Further,this type of liquid crystal very quickly assumes either one of theabove-mentioned two stable states in reply to an electric field appliedthereto and retains the state in the absence of an electric field. Byutilizing these properties, essential improvements can be attained withrespect to the above-mentioned difficulties involved in the conventionalTN-type liquid crystal device. This point will be explained hereinafterin further detail in connection with the present invention.

However, in order that an optical modulation device using the liquidcrystal having bistability could show desired operation performances,the liquid crystal interposed between a pair of parallel base plates isrequired to be placed in such a state of molecular arrangement that thetransition between the two stable states can effectively occur, as amatter different from, or a precondition of, the application of anelectric field. With respect to, for example, a ferroelectric liquidcrystal having an SmC* or other phases, there must be formed amonodomain wherein the layers of the liquid crystal molecules areperpendicular to the face of the base plate and therefore the axes ofthe liquid crystal molecules are almost in parallel with the base plateface. However, in the optical modulation devices using a bistable liquidcrystal, and orientation or alignment state of a liquid crystal havingsuch a monodomain structure cannot satisfactorily be formed, whereby theoptical modulation device cannot actually show sufficient performances.

For example, several methods have been proposed to give such anorientation state, including a method of applying a magnetic field and amethod of applying a shearing force. These methods have not necessarilyprovided satisfactory results. For example, the method of applying amagnetic field requires a large size of apparatus and is not readilycompatible with a thin layer cell which is generally excellent inoperation performances. On the other hand, the method of applying ashearing force is not compatible with a process where a cell structureis first formed and then a liquid crystal is poured thereinto.

SUMMARY OF THE INVENTION

A principal object of the present invention is, in view of theabove-mentioned circumstances, to provide an improvement in monodomainformability or initial alignment, of which an improvement has beendesired, to an optical modulation device suing a bistable liquidcrystal, which is potentially suited for a display device with a highresponse speed, picture elements arranged at a high density and a largedisplay area or an optical shutter having a high shutter speed, therebyto allow the optical modulation device to fully exhibit their excellentcharacteristics.

We have made a further study with the above object, noting theorientation characteristics of a liquid crystal during a temperaturedecreasing stage for causing transition from another phase (e.g., ahigher temperature phase such as an isotropic phase) of the liquidcrystal to lower temperature phase such as a smectic phase, e.g., SmA(smectic A phase). As the result, we have observed that a monodomainwhere liquid crystal molecules of, e.g., smectic A phase are aligned inone direction can be formed by using a liquid crystal compositioncomprising a liquid crystal showing at least a chiral smectic phase suchas chiral smectic C (SmC*) phase, chiral smectic H (SmH*) phase, chiralsmectic F (SmF*) phase, chiral smectic I (SmI*) phase or chiral smecticG (SmG*) phase and a liquid crystal showing at least a cholestericphase, and by imparting a function of orienting molecular axes of theliquid crystal molecules preferentially in one direction to a face of abase plate contacting the liquid crystal composition, whereby a liquidcrystal device having operation characteristics based on the bistabilityof the liquid crystal and a monodomain formation characteristic of theliquid crystal layer in combination is provided.

According to the present invention based on the above finding, there isprovided a liquid crystal device, comprising: (a) a pair of base plateseach having an orientation control film thereon, and (b) a liquidcrystal composition interposed between the base plates; said liquidcrystal composition comprising a mixture including at least one liquidcrystal compound which has a temperature range in which it shows chiralsmectic phase and at least one optically active substance which does nothave a temperature range in which it shows chiral smectic phase; saidliquid crystal composition having a temperature range in which it showscholesteric phase and being placed in chiral smectic phase which hasbeen formed through cholesteric phase on temperature decrease; saidliquid crystal composition comprising liquid crystal molecules havinglong axes forming a pre-tilt in the chiral smectic phase.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are schematic perspective views illustrating the basicoperation principle of a liquid crystal cell used in the presentinvention,

FIG. 3A is a plan view showing an example of the liquid crystal deviceaccording to the present invention, FIG. 3B is a sectional view takenalong the line 3B--3B in FIG. 3A,

FIG. 4 is a sectional view showing another example of the liquid crystaldevice according to the present invention,

FIG. 5 is a sectional view schematically showing a tilt or oblique vapordeposition apparatus for use in production of the liquid crystal deviceaccording to the present invention,

FIG. 6 is a schematic plan view showing an electrode arrangement of aliquid crystal device used in the present invention,

FIGS. 7A to 7D illustrate signals for driving a liquid crystal deviceused in the present invention,

FIGS. 8A to 8D illustrate waveforms applied to respective pictureelements,

FIG. 9A is a sectional view of an oblique deposited orientationcontrolling film formed on a base plate; FIG. 9B is a sectional view ofsuch an obliquely deposited orientation controlling film carrying liquidcrystal molecules in an aligned form in cholesteric or smectic A phase.,FIG. 9C is a plan view corresponding to FIG. 9B; and FIG. 9D is asectional view of such an obliquely deposited orientation controllingfilm carrying liquid crystal molecules in chiral smectic C phase.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The liquid crystal composition used in the present invention is onewhich comprises a liquid crystal showing at least a chiral smectic phasesuch as SmC*, SmH*, SmF*, SmI* or SmG* and a liquid crystal showing atleast a cholesteric phase and shows a ferroelectricity.

Specific examples of the liquid crystal showing a chiral smectic phaseand the liquid crystal showing a cholesteric phase available for thepresent invention are shown in Table 1 and Table 2, respectively.

                                      TABLE 1                                     __________________________________________________________________________    Specific examples of liquid crystal showing chiral smetic phase               (compound name, structural formula and phase transition                       __________________________________________________________________________    temperature)                                                                  (1)                                                                            ##STR1##                                                                     p-decyloxybenzylidene-p'-amino-2-methylbutyl                                  cinnamate (DOBAMBC)                                                            ##STR2##                                                                     (2)                                                                            ##STR3##                                                                     p-hexaloxybenzylidene-p'-amino-2-chloropropyl                                 cinnamate (HOBACPC)                                                            ##STR4##                                                                     (3)                                                                            ##STR5##                                                                     p-decyloxybenzylidene-p'-amino-2-methylbutyl-α-                         cyanocinnamate (DOBAMBCC)                                                      ##STR6##                                                                     (4)                                                                            ##STR7##                                                                     p-tetradecyloxybenzylidene-p'-amino-2-methylbutyl-α-                    cyanocinnamate (TDOBAMBCC)                                                     ##STR8##                                                                     (5)                                                                            ##STR9##                                                                     p-octyloxybenzylidene-p'-amino-2-methylbutyl-α-                         chlorocinnamate (DOOBAMBCC)                                                    ##STR10##                                                                    (6)                                                                            ##STR11##                                                                    p-octyloxybenzylidene-p'-amino-2-methylbutyl-α-                         methylcinnamate                                                                ##STR12##                                                                    (7)                                                                            ##STR13##                                                                    4-4'-azoxycinnamic acid-bis(2-methylbutyl)ester                                ##STR14##                                                                    (8)                                                                            ##STR15##                                                                    4-O-(2-methyl)-butylresorcylidene-4'-octylaniline                             (MBRA 8)                                                                       ##STR16##                                                                    __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        Specific examples of optically active substances                              not showing chiral smectic phase but showing                                  cholesteric phase (compound name, structured                                  formula and phase transition temperature)                                     ______________________________________                                        (A) Chloesteryl propionate                                                     ##STR17##                                                                    (B) Cholesteryl nonanate                                                       ##STR18##                                                                    (C) Cholesteryl palmitate                                                      ##STR19##                                                                    (D) Cholesteryl benzoate                                                       ##STR20##                                                                    (E)                                                                            ##STR21##                                                                    4-(2"-methylbutyl)-4'-cyanobiphenyl                                            ##STR22##                                                                    (G)                                                                            ##STR23##                                                                    4-octylphenyl-4'-(4-β-methylbenzoyloxy)benzoate                           ##STR24##                                                                    (H)                                                                            ##STR25##                                                                    4-cyanobenzylidene-4'-(2-methylbutyl)aniline                                   ##STR26##                                                                    (I)                                                                            ##STR27##                                                                    3-(2-methylbutyl)-4'-hexyloxyazobenzene                                        ##STR28##                                                                    (J)                                                                            ##STR29##                                                                    4-(2-methylbutyl)phenyl-4'-decyloxybenzoate                                    ##STR30##                                                                    (K)                                                                            ##STR31##                                                                    4-hexyloxy-4'-(2-methylbutyl)benzoate                                          ##STR32##                                                                    ______________________________________                                    

The above-mentioned liquid crystals showing a chiral smectic phase andliquid crystals showing a cholesteric phase may respectively be used incombination of two or more species from each group.

While the proportion between the two types of liquid crystals can varydepending on particular liquid crystals used, the liquid crystal showinga cholesteric phase may generally be used in an amount of 0.1 to 50parts by weight, preferably 1 to 20 parts by weight with respect to 100parts by weight of the liquid crystal showing a chiral smectic phase.

In a preferred embodiment, a liquid crystal causing successive phasetransition of isotropic phase, cholesteric phase, SmA phase and chiralsmectic phase, in the order named, on temperature decrease, may be usedin place of the liquid crystals shown in Table 1. Specific examples ofsuch a liquid crystal are enumerated in Table 3 below.

                  TABLE 3                                                         ______________________________________                                        Specific examples of liquid crystal showing                                   chiral smectic phase (compound name, structural                               formula and phase transition temperature)                                     ______________________________________                                        (1)                                                                            ##STR33##                                                                    4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-                               carboxylate                                                                    ##STR34##                                                                     ##STR35##                                                                    (2)                                                                            ##STR36##                                                                    4-heptylphenyl-4-(4"-methylhexyl)biphenyl-4'-                                 carboxylate                                                                    ##STR37##                                                                     ##STR38##                                                                    (3)                                                                            ##STR39##                                                                    p-n-octyloxybenzoic acid-p'-(2-methylbutyloxy)-                               phenyl ester                                                                   ##STR40##                                                                     ##STR41##                                                                    ______________________________________                                    

The liquid crystals shown in Table 3 may also be used in two or morespecies in combination.

In another preferred embodiment of the present invention, a liquidcrystal causing successive phase transition of isotropic phase,cholesteric phase and chiral smectic phase, in the order named, ontemperature decrease, may be used in place of the liquid crystalsshowing chiral smectic phase as mentioned above. Specific examples ofsuch a liquid crystal are enumerated in Table 4 below.

                                      TABLE 4                                     __________________________________________________________________________    Specific examples of liquid crystals showing chiral smectic phase             (compound name, structural formula and phase transition                       __________________________________________________________________________    temperature)                                                                  (1)                                                                            ##STR42##                                                                    4-hexyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-                               carboxylate                                                                    ##STR43##                                                                    (2)                                                                            ##STR44##                                                                    4-octyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-                               carboxylate                                                                    ##STR45##                                                                    (3)                                                                            ##STR46##                                                                     ##STR47##                                                                     ##STR48##                                                                    __________________________________________________________________________

The liquid crystals of the type as shown in the Table 4 may be used incombination of two or more species.

According to still another preferred embodiment of the presentinvention, the liquid crystal composition is composed as a ferroelectriccomposition comprising at least two liquid crystals which show at leasta chiral smectic phase; at least one of the liquid crystals showingfurther a cholesteric phase. More specifically the chiral smectic phasemay be SmC*, SmF*, SmI* or SmG*.

Specific examples of the liquid crystals constituting this embodiment ofthe liquid crystals are shown in Tables 1, 3 and 4 described above.These liquid crystals selected from each group may also be used incombination of two or more species.

In this embodiment of the composition, while the proportion of the twotypes of the liquid crystals can vary depending on particular liquidcrystals used, the liquid crystal showing cholesteric phase as well as achiral smectic phase may generally be used in a proportion of 0.1 to 50parts by weight, preferably 0.1 to 10 parts by weight, with respect to 1part by weight of the liquid crystal showing a chiral smectic phase butnot a cholesteric phase.

According to a further preferred embodiment of the present invention,the liquid crystal composition may be composed of a combination of aliquid crystal (referred to as "liquid crystal A") causing successivephase transition of isotropic phase, cholesteric phase, smectic A phaseand chiral smectic phase (inclusive of SmC*, SmH*, SmF*, SmI*, SmJ*,SmK*, SmI*, SmG*) in the order named on temperature decrease, and aliquid crystal (referred to as "liquid crystal B") causing successivephase transition of isotropic phase, cholesteric phase and chiralsmectic phase. Specific examples of the liquid crystals A and B areshown in Tables 3 and 4, respectively. The composition of thisembodiment, when sandwiched between base plates to a face of which hasbeen imparted a function of orienting molecular axes of the liquidcrystal molecules preferentially in one direction, provides a monodomainwherein liquid crystal molecules are aligned uniformly in one direction,whereby a liquid crystal device having operation characteristics basedon the bistability of the liquid crystal and a monodomain formationcharacteristic of the liquid crystal layer in combination is provided.

In this embodiment, a composition further comprising a liquid crystal(referred to as "liquid crystal C") which causes successive phasetransition of isotropic phase, smectic phase and chiral smectic phase,in the order named, on temperature decrease, provides a still betterorientation stability for a longer period of time than theabove-mentioned composition.

The liquid crystal device according to this embodiment of the inventionmay be expressed as one comprising a pair of base plates and a liquidcrystal composition interposed therebetween; the liquid crystalcomposition comprising a liquid crystal A, a liquid crystal B and,preferably, a liquid crystal C; a face of at least one of the pair ofbase plates having been provided with a function of preferentiallyorienting the axes of the liquid crystal molecules contacting the facein one direction.

The proportions of the liquid crystals A and B in the liquid crystalcomposition can vary depending on particular liquid crystals used butgenerally be such that the liquid crystal A is used in 0.05 to 20 partsby weight, preferably 0.5 to 2 parts by weight with respect to 1 part byweight of the liquid crystal B. The proportion of the liquid crystal C,when used, is such that it constitutes 0.1 to 40% by weight, preferably5 to 20% by weight, of the resultant liquid crystal composition.

The liquid crystal composition according to the present invention maypreferably be so composed that it will because successive phasetransition of isotropic phase, cholesteric phase, smectic A phase andchiral smectic phase, in the order named, on temperature decrease.

When a device is constituted using these materials, the device may besupported with a block of copper, etc., in which a heater is embedded inorder to realize a temperature condition where the liquid crystalcomposition assumes a desired chiral smectic phase.

Referring to FIG. 1, there is schematically shown an example of aferroelectric liquid crystal cell for explanation of the operationthereof. Reference numerals 11 and 11a denote base plate (glass plates)on which a transparent electrode of, e.g., In₂ O₃, SnO₂, ITO (Indium-TinOxide), etc., is disposed respectively. A liquid crystal of a chiralsmectic phase such as SmC*, SmH*, SmF*, SmI* or SmG* in which liquidcrystal molecular layers 12 are oriented perpendicular to surfaces ofthe glass plates is hermetically disposed therebetween. A full line 13shows liquid crystal molecules. Each liquid crystal molecule 13 has adipole moment (P.sub.⊥) 14 in a direction perpendicular to the axisthereof. When a voltage higher than a certain threshold level is appliedbetween electrodes formed on the base plates 11 and 11a, a helicalstructure of the liquid crystal molecule 13 is loosened or unwound tochange the alignment direction of respective liquid crystal molecules 13so that the dipole moment (P.sub.⊥) 14 ar all directed in the directionof the electric field. The liquid crystal molecules 13 have an elongatedshape and show refractive anisotropy between the long axis and the shortaxis thereof. Accordingly, it is easily understood that when, forinstance, polarizers arranged in a cross nicol relationship, i.e., withtheir polarizing directions crossing each other, are disposed on theupper and the lower surfaces of the glass plates, the liquid crystalcell thus arranged functions as a liquid crystal optical modulationdevice of which optical characteristics vary depending upon the polarityof an applied voltage.

The liquid crystal layer in the liquid crystal device of the presentinvention may be rendered sufficiently thin in thickness (e.g., lessthan 10 μ). As the thickness of the liquid crystal layer is decreased,the helical structure of the liquid crystal molecules is loosened evenin the absence of an electric field whereby the dipole moment assumeseither of the two states, i.e., P in an upper direction 24 or Pa in alower direction 24a as shown in FIG. 2. When electric field E or Eahigher than a certain threshold level and different from each other inpolarity as shown in FIG. 2 is applied to a cell having theabove-mentioned characteristics, the dipole moment is directed either inthe upper direction 24 or in the lower direction 24a depending on thevector of the electric field E or Ea. In correspondence with this, theliquid crystal molecules are oriented in either of a first stable state23 and a second stable state 23a.

When the above-mentioned ferroelectric liquid crystal is used as anoptical modulation element, it is possible to obtain two advantages asbriefly touched on hereinbefore. First is that the response speed isquite fast. Second is that the orientation of the liquid crystal showsbistability. The second advantage will be further explained, e.g., withreference to FIG. 2. When the electric field E is applied to the liquidcrystal molecules, they are oriented in the first stable state 23. Thisstate is kept stable even if the electric field is removed. On the otherhand, when the electric field Ea of which direction is opposite to thatof the electric field E is applied thereto, the liquid crystal moleculesare oriented to the second stable state 23a, whereby the directions ofmolecules are changed. This state is similarly kept stable even if theelectric field is removed. Further, as long as the magnitude of theelectric field E being applied is not above a certain threshold value,the liquid crystal molecules are placed in the respective orientationstates. In order to effectively realize high response speed andbistability, it is preferable that the thickness of the cell is as thinas possible.

The most serious problem encountered in forming a device using such aferroelectric liquid crystal has been, as briefly mentionedhereinbefore, that it is difficult to form a cell having a highlyuniform monodomain wherein liquid crystal layers having a chiral smecticphase such as SmC*, SmH*, SmF*, SmI* or SmG* are aligned perpendicularto the base plate phases and the liquid crystal molecules are alignedalmost in parallel with the base plate phases. A principal object of theinvention is to provide a solution to this problem.

FIGS. 3A and 3B illustrate an example of the liquid crystal deviceaccording to the present invention. FIG. 3A is a plan view of theexample and FIG. 3B is a sectional view taken along the line 3B--3B inFIG. 3A.

A cell structure 100 shown in FIG. 3 comprises a pair of base plates 101and 101a made of glass plates or plastic plates which are held with apredetermined gap with spacers 104 and sealed with an adhesive 106 toform a cell structure. On the base plate 101 is further formed anelectrode group (e.g., an electrode group for applying scanning voltagesof a matrix electrode structure) comprising a plurality of transparentelectrodes in a predetermined pattern, e.g., of a stripe pattern. On thebase plate 101 is formed another electrode group (e.g., an electrodegroup for applying signal voltages of the matrix electrode structure)comprising a plurality of transparent electrodes 102a crossing thetransparent electrodes 102.

On the base plate provided with such transparent electrodes may befurther formed an orientation controlling film 105 composed of aninorganic insulating material such as silicon monoxide, silicon dioxide,aluminum oxide, zirconia, magnesium fluoride, cerium oxide, ceriumfluoride, silicon nitride, silicon carbide, and boron nitride, or anorganic insulating material such as polyvinyl alcohol, polyimide,polyamide-imide, polyester-imide, polyparaxylylene, polyester,polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide,polystyrene, cellulose resin, melamine resin, urea resin and acrylicresin.

The orientation controlling film 105 may be formed by first forming afilm of an inorganic insulating material or an organic insulatingmaterial as described above and then rubbing the surface thereof in onedirection with velvet, cloth, paper, etc.

In another preferred embodiment according to the present invention, theorientation controlling film 105 may be formed as a film of an inorganicinsulating material such as SiO or SiO₂ on the base plate 101a by theoblique or tilt vapor deposition.

In an apparatus shown in FIG. 5, a bell jar 501 is placed on aninsulating base plate 503 provided with a suction hole 505 and the belljar 501 is made vacuum by operating a vacuum pump (not shown) connectedthe suction hole 505. A crucible 507 made of tungsten or molybdenum isplace inside and at the bottom of the bell jar 501. In the crucible 507is paced several grams of a crystal such as SiO, SiO₂ or MgF₂. Thecrucible 507 has two downwardly extending arms 507a and 507b, which arerespectively connected to lead wires 509 and 510. A power source 506 anda 504 are connected in series to the lead wires 509 and 510 outside thebell jar 501. A base plate 502 is disposed inside the bell jar 501 andright above the crucible 507 so that it forms an angle of θ with respectto the vertical axis of the bell jar 501.

First, the bell jar 501 is evacuated to a vacuum of about 10⁻⁵ mmHgwhile the switch 504 is open. Then the switch 504 is closed to supply apower while adjusting an output of the power source 506 until thecrucible is heated to an incandescent state of an appropriatetemperature for evaporating the crystal 508. About 100 amps. of currentis required for giving an appropriate temperature range (700°-1000° C.).The crystal 508 is then evaporated off to form an upward molecularstream denoted by S in the figure. The stream S is incident on the baseplate 502 with an angle thereto of θ (about 35 degrees) to coat the baseplate 502. The angle θ is the above mentioned incident angle and thedirection of the stream S in the "oblique or tilt vapor depositiondirection". The thickness of the film is determined base on thecalibration of the thickness with respect to the operation time which iseffected prior to the introduction of the base plate 502 into the belljar 501. After an appropriate thickness of the film is formed, a powersupply from the source 506 is decreased, the switch 504 is opened, andthe bell jar 501 and the interior thereof are cooled. Then, the pressurein the bell jar is raised to atmospheric pressure and the base plate 502is taken out from the bell jar 501.

The above-described oblique vapor deposition process using an apparatusshown in FIG. 5 provides an orientation controlling film 90 on asubstrate 92 having a cross-sectional shape as shown in FIG. 9A. Theorientation controlling film 90 has a function of aligning ororientating molecular axes 91 of a cholesteric liquid crystal or asmectic A liquid crystal in parallel with a wedge or stripe-shapedpattern 94 of the film 90 as shown in FIGS. 9B and 9C. A chiral smecticliquid crystal may be formed by cooling from its cholesteric phase orsmectic A phase, and liquid crystal molecules in the chiral smecticphase are caused to have molecular long axes 92 tilted from themolecular long axes 91 in the smectic A phase. The molecular long axes92 are aligned on slopes of the obliquely deposited orientationcontrolling film 90 as shown in FIG. 9D to provide a pretilt inherent tosuch an obliquely deposited orientation controlling film 90. The angleof such a pre-tilt may be generally 5 degrees or higher, preferably 5-45degrees.

In still another embodiment, the orientation controlling film 105 may beformed by first forming a uniform film of the above-mentioned inorganicor organic insulating material on, i.e., in contact with or above, thebase plate 101a and then subjecting the surface of the film to theoblique or tilt etching to provide the surface with an orientationcontrolling effect.

It is preferred that the orientation controlling film 105 is also causedto function as an insulating film. For this purpose, the orientationcontrolling film may preferably have a thickness in the range of 100 Åto 1 μ, especially 500 Å to 5000 Å. The insulating film also has afunction of preventing the occurrence of an electric current which isgenerally caused due to minor quantities of impurities contained in theliquid crystal layer 103, whereby deterioration of the liquid crystalcompounds is prevented even after repeated operations.

In the liquid crystal device according to the present invention, it ispossible to form an orientation controlling film similar to theorientation controlling film 105 also on the other base plate 101.

A similar orientation controlling effect can also be imparted to theside walls of spacers 104 in the structure shown in FIG. 3, for example,by rubbing.

In the cell structure shown in FIG. 3, the liquid crystal layer 103 maybe formed into a chiral smectic phase such as SmC*, SmH*, SmF*, SmI* orSmG*. The liquid crystal layer 103 having a chiral smectic phase isformed by first forming an SmA (smectic A) phase through phasetransition from a cholesteric phase, particularly a cholesteric phasewith a grandjean texture, on cooling and by further phase transition oncooling into a chiral smectic phase such as SmC* or SmH*.

One important aspect of the present invention is that, when a liquidcrystal composition containing a liquid crystal showing a cholestericphase is transformed from a higher temperature phase into SmA phase, theaxes of the liquid crystal molecules of the SmA phase are aligned ororiented in the orientation controlling direction imparted to theorientation controlling film, whereby a uniform monodomain is formed.

FIG. 4 shows another embodiment of the liquid crystal device accordingto the present invention. In the liquid crystal device shown in FIG. 4,a plurality of spacer members 201 are disposed between a pair of baseplates 101 and 101a. The spacer members 201 can be provided, forexample, by forming a film of an inorganic compound such as SiO, SiO₂,Al₂ O₃ and TiO₂, or a resin such as polyvinyl alcohol, polyimide,polyamide-imide, polyester-imide, polyparaxylylene, polyester,polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate,polyamide, polystyrene, cellulose resin, melamine resin, urea resin,acrylic resin and a photoresist resin on the base plate 101 on which anorientation controlling film 105 has not been provided, and by etchingthe film to leave the spacer members 201 at appropriate parts.

A similar orientation effect as explained with reference to the surfaceof the base plate 101 or 101a can also be imparted to the side wall ofthe spacer members 104 and 201.

Such a cell structure 100 having base plates 101 and 101a as shown inFIG. 3 or FIG. 4 is sandwiched between a pair of polarizers 107 and 108to form an optical modulation device causing optical modulation when avoltage is applied between electrodes 102 and 102a.

Next, a process for producing the liquid crystal device according to thepresent invention by orientation-controlling the liquid crystal layer103 is explained more specifically, with reference to FIG. 3.

First, a cell 100 containing a liquid crystal according to the presentinvention is set in such a heating case (not shown) that the whole cell100 is uniformly heated therein. Then, the cell 100 is heated to atemperature where the liquid crystal in the cell assumes as isotropicphase. The temperature of the heating case is decreased, whereby theliquid crystal composition is subjected to a temperature decreasingstage. In the temperature decreasing stage, the liquid crystalcomposition in the isotropic phase is transformed into SmA eitherdirectly or through a cholesteric phase having a grandjean texture.Herein, the axes of the liquid crystal molecules in the SmA phase arealigned in the rubbing direction.

Then, the liquid crystal in the SmA phase is transformed into a chiralsmectic phase such as SmC* on further cooling, whereby a monodomain ofthe chiral smectic phase with a non-spiral structure is formed if thecell thickness is of the order of, for example, 1 μm.

Referring to FIG. 6, there is schematically shown an example of a cell41 having a matrix electrode arrangement in which a ferroelectric liquidcrystal compound is interposed between a pair of groups of electrodesoppositely spaced from each other. Reference numerals 42 and 43respectively denote a group of scanning electrodes to which scanningsignals are applied and a group of signal electrodes to whichinformation signals are applied. Referring to FIGS. 7A and 7B, there arerespectively shown electric signals applied to a selected scanningelectrode 42(s) and electric signals applied to the other scanningelectrodes (non-selected scanning electrodes) 42(n). On the other hand,FIGS. 7C and 7D show electric signals applied to the selected signalelectrode 43(s) and electric signals applied to the non-selected signalelectrodes 43(n), respectively. In FIGS. 7A to 7D, the abscissa and theordinate represent a time and a voltage, respectively. For instance,when displaying a motion picture, the group of scanning electrodes 42are sequentially and periodically selected. If a threshold voltage forgiving a first stable state of the liquid crystal having bistability isreferred to as V_(th1) and a threshold voltage for giving a secondstable state thereof as -V_(th2), an electric signal applied to theselected scanning electrode 42(s) is an alternating voltage showing V ata phase (time) t₁ and -V at a phase (time) t₂, as shown in FIG. 7A. Theother scanning electrodes 42(n) are grounded as shown in FIG. 7B.Accordingly, the electric signals appearing thereon show zero volt. Onthe other hand, an electric signal applied to the selected signalelectrode 43(s) shows V as indicated in FIG. 7C while an electric signalapplied to the non-selected signal electrode 43(n) shows -V as indicatedin FIG. 7D. In this instance, the voltage V is set to a desired valuewhich satisfies V<V_(th1) <2V and -V>-V_(th2) >-2V. Voltage waveformsapplied to each picture element when such electric signals are given areshown in FIG. 8. Waveforms shown in FIGS. 8A, 8B, 8C and 8D correspondto picture elements A, B, C and D shown in FIG. 6, respectively. Namely,as seen from FIG. 8A, a voltage of 2 V above the threshold level V_(th1)is applied to the ferroelectric liquid crystal electrically connected tothe picture elements A on the selected scanning line at a phase of t₂.Further, a voltage of -2 V above the threshold level -V_(th2) is appliedto the ferroelectric liquid crystal electrically connected to thepicture elements B on the same scanning line at a phase of t₁.Accordingly, depending upon whether a signal electrode is selected ornot on a selected scanning electrode line, the orientation of liquidcrystal molecules changes. Namely, when a certain signal electrode isselected, the liquid crystal molecules are oriented to the first stablestate, while when not selected, are oriented to the second stable state.In either case, the orientation of the liquid crystal molecules is notrelated to the previous states of each picture element.

On the other hand, as indicated by the picture elements C and D on thenon-selected scanning lines, a voltage applied to all picture elements Cand D is +V or -V, each not exceeding the threshold level. Accordingly,the ferroelectric liquid crystal molecules electrically connected to therespective picture elements C and D are placed in the orientationscorresponding to signal states produced when they have been last scannedwithout change in orientation. Namely, when a certain scanning electrodeis selected, signals corresponding to one line are written and thuswriting of signals corresponding to one frame is completed. The signalstate of each picture element can be maintained until the line issubsequently selected. Accordingly, even if the number of scanning linesincreases, the duty ratio does not substantially change, resulting in nopossibility of lowering in contrast, occurrence of crosstalk, etc. Inthis instance, the magnitude of the voltage V and length of the phase(t₁ +t₂)=T usually ranges from 3 volts to 70 volts and from 0.1 μsec to2 msec, respectively, although they change depending upon the thicknessof a liquid crystal material or a cell used. In this way, the electricsignals applied to a selected scanning electrode can cause eitherdirection of change in state, i.e., from a first stable state (definedherein as "bright" state when converted to corresponding opticalsignals) to a second stable state (defined as "dark" state whenconverted to corresponding optical signals), or vice versa.

Compared with a case where a liquid crystal showing a chiral smecticphase such as DOBAMBC, HOBACPC, or MBRA 8 is used alone, the liquidcrystal composition used in the present invention containing a liquidcrystal showing a cholesteric phase has a better orientationcharacteristic and gives an orientation or alignment state free oforientation defects.

As for the extent of orientation controlling treatment, it is preferredto impart such as orientation controlling treatment or layer to only oneof the pair of base plates in order to give a faster response speedbecause a weaker constraining force acting on liquid crystal moleculeson the surface of the base plate (or a weaker orientation controllingeffect imparted to the base plate) favors a better switchingcharacteristic (faster response speed), especially when a thin cell isused or a chiral smectic phase such as SmC*, SmH*, SmF*, SmI* or SmG*having bistability (memory characteristic) is formed. For example, withrespect to a cell having a thickness of 2 μm or less, a cell in whichonly one base plate has been subjected to orientation controllingtreatment gives about twice as fast a response speed as that obtained bya cell in which both base plates have been treated for orientationcontrol.

The present invention will be further explained with reference toworking examples.

EXAMPLE 1

On a square glass base plate were formed ITO (Indium-Tin-Oxide)electrode films in the form of stripes with a width of 62.5 μm at apitch of 100 μm. In an apparatus for the oblique vapor deposition asshown in FIG. 5, the base plate was disposed with its face having theITO film being directed downward and a crystal of SiO₂ was set in acrucible of molybdenum. Then the vapor deposition apparatus wasevacuated to a vacuum of the order of 10⁻⁵ mmHg and SiO₂ was obliquelyvapor-deposited in a prescribed manner to form an electrode plate withan 800 μ-thick oblique vapor deposition film (A electrode plate).

On the other hand, on a similar glass plate provided with stripe-formITO electrode films was applied a polyimide-forming solution ("PIQ":polyimide-isoindolquinazoline-dione, produced by Hitachi Kasei Kogyo K.K.; Non-volatile content: 14.5 wt. %) by means of a spinner coater,which was then heated at 80° C. for 30 minutes, at 200° C. for 60minutes and at 350° C. for 30 minutes to form a film of 800 Å inthickness (B electrode plate).

Then, a heat-setting epoxy adhesive was applied to the periphery of theA electrode plate except for the portion forming an injection port byscreen printing process. The A electrode plate and the B electrode platewere superposed with each other so that their stripe-pattern electrodescrossed each other with right angles and secured to each other with apolyimide spacer while leaving the gap of 2 μ therebetween, thereby toform a cell (blank cell).

Separately, a liquid crystal composition was prepared by mixing 5 partsby weight of cholesteryl nonanate with 100 parts by weight ofp-decyloxy-benzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC).

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port of the above-prepared cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and, at a constant temperatureof bout 70° C., was observed through a microscope while being sandwichedbetween a pair of polarizers arranged in the cross nicol relationship,whereby a monodomain of SmC* phase whose spiral had been loosened wasfound to be formed.

EXAMPLE 2

On a square glass plate provided with stripe-form ITO electrode films asused in Example 1 was applied a polyimide-forming solution ("PIQ",produced by Hitachi Kasei Kogyo K. K.; Non-volatile content: 14.5 wt. %)by means of a spinner coater, which was then heated at 80° C. for 30minutes, at 200° C. for 60 minutes and at 350° C. for 30 minutes to forma film of 800 Å in thickness (A electrode plate).

A similar electrode plate provided with a polyimide film was subjectedto a rubbing treatment to produce a B electrode plate.

Then, a heat-setting epoxy adhesive was applied to the periphery of theA electrode plate except for the portion forming an injection port byscreen printing process. The A electrode plate and the B electrode platewere superposed with each other so that their stripe-pattern electrodescrossed each other with right angles and secured to each other with apolyimide spacer while leaving the gap of 2 μ therebetween, thereby toform a cell (black cell).

Separately, a liquid crystal composition was prepared by mixing 10 partsby weight of 4-(2-methylbutyl)phenyl-4'-decyloxybenzoate with 100 partsby weight of DOBAMBC.

The liquid crystal composition was heated into the isotropic phase andinjected through the infection port of the above-prepared cell, and theinfection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5°/hr and, at a constant temperature ofabout 65° C., was observed through a microscope while being sandwichedbetween a pair of polarizers arranged in the cross nicol relationship,whereby a monodomain of an SmC* phase whose spiral had been loosened wasfound to be formed.

EXAMPLE 3

A blank cell as used in Example 1 was provided.

Separately, a liquid crystal composition was prepared by mixing 8 partsby weight of 4-hexyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-carboxylatewith 100 parts by weight of DOBAMBC.

The liquid crystal composition was heated into the isotropic phase andinfected through the injection port of the above-prepared cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phasewhose spiral had been loosened was found to be formed.

EXAMPLE 4

A blank cell as used in Example 1 was provided.

Separately, a liquid crystal composition was prepared by mixing 5 partsby weight of 4-heptylphenyl-4-(4"-methylhexyl)biphenyl-4'-carboxylatewith 100 parts by weight of DOBAMBC.

The liquid crystal composition was heated into the isotropic phase andinfected through the infection port of the above-provided cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phasewhose spiral had been loosened was found to be formed.

EXAMPLE 5

A blank cell as used in Example 1 was provided.

Separately, a liquid crystal composition was prepared by mixing 5 partsby weight of cholesteryl nonanate with 100 parts by weight of4-hexyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port of the above-provided cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phase withnon-spiral structure was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 500 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as a comparative experiment, a liquid crystal devicewas prepared in the same manner as described above except that thecholesteryl nonanate was omitted. The liquid crystal device wassubjected to similar microscopic observation. As a result, a monodomainof SmC* phase with non-spiral structure was found to be formed at theinitial stage whereas the monodomain of SmC* phase was not retainedafter the 500 hours of durability test.

EXAMPLE 6

A blank cell as used in Example 2 was provided.

Separately, a liquid crystal composition was prepared by mixing 10 partsby weight of 4-(2-methylbutyl)phenyl-4'-decyloxybenzoate with 100 partsby weight of 4-octyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port of the above provided cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and, at a constant temperatureof about 65° C., was observed through a microscope while beingsandwiched between a pair of polarizers arranged in the cross nicolrelationship, whereby a monodomain of SmC* phase whose spiral had beenloosened was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 700 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as a comparative experiment, a liquid crystal devicewas prepared in the same manner as described above except that the4-(2-methylbutyl)-phenyl-4'-decyloxybenzoate was omitted. The liquidcrystal device was subjected to similar microscopic observation. As aresult, a monodomain of SmC* phase with non-spiral structure was foundto be formed at the initial stage whereas the monodomain of SmC* phasewas not retained after the 700 hours of durability test.

EXAMPLES 7-9

Liquid crystal devices were prepared in the same manner as in Example 6except that the 4-(2-methylbutyl)phenyl-4'-decyloxybenzoate was replacedby 4-(2"-methylbutyl)4'-cyanobiphenyl (Example 7), cholesteryl benzoate(Example 8) and 4-(2"-methylbutyloxy)4'-cyanobiphenyl (Example 9),respectively. The liquid crystal devices were subjected to similarmicroscopic observation, whereby a monodomain of SmC* with non-spiralstructure was respectively found to be formed and observed to beretained after the 700 hours of the durability test as carried out inExample 6.

EXAMPLE 10

A transparent electrode film consisting primarily of indium oxide wasformed on a polyethylene terephthalate base film of 100 μm in thicknesswith the surface temperature of the base film being suppressed to below120° C. by means of a low-temperature sputtering apparatus, thereby toprovide a plastic substrate. A solution having the following composition(Solution Composition (1)) was applied on the plastic substrate anddried at 120° C. for 30 minutes to form a coating film

    ______________________________________                                        Solution composition (1)                                                      ______________________________________                                        Acetomethoxyaluminum diisopropylate                                                                  1         g                                            Polyester resin (Bylon 30P, mfd. by                                                                  0.5       g                                            Toyobo K.K.)                                                                  Tetrahydrofuran        100       ml                                           ______________________________________                                    

The coating film on the plastic substrate was then rubbed in onedirection under the pressure of 100 g/cm². A pair of the thusrubbing-treated plastic substrate were superposed with each other sothat their rubbing directions were in parallel with each other andsecured to each other with a gap of 1 μ therebetween by sealing theperiphery except for a port for liquid crystal injection, whereby ablank cell was prepared

Separately, a liquid crystal composition was prepared by mixing 4 partsby weight of 4-(2-methylbutyl)-4'-hexyloxyazobenzene with 100 parts byweight of 4-hexyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port and into the above-provided cellunder vacuum, and the injection port was sealed. The liquid crystal cellthus formed was gradually cooled at a rate of 0.5° C./hr and wasobserved through a microscope while being sandwiched between a pair ofpolarizers arranged in the cross nicol relationship, whereby amonodomain of SmC* phase with non-spiral structure was found to beformed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 500 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was observed to be retained.

On the other hand, as a comparative experiment, a liquid crystal devicewas prepared in the same manner as described above except that the4-(2-methylbutyl)-4'-hexyloxyazobenzene was omitted. The liquid crystaldevice was subjected to similar microscopic observation. As a result, amonodomain of SmC* phase with non-spiral structure was found to beformed at the initial stage, whereas the monodomain of SmC* phase wasnot retained after the 500 hours of durability test.

EXAMPLE 11

A glass plate, on which stripes of ITO electrode film were provided in awidth of 62.5 μm and at a pitch of 100 μm, was further coated with acoating solution having the following solution composition (6).

    ______________________________________                                        Solution composition (6)                                                      ______________________________________                                        Tetraisopropoxytitanium                                                                              1        g                                             Condensation product of pyromellitic                                                                 0.5      g                                             anhydride and 4,4'-diaminodiphenyl                                                                   (solid)                                                ether as a polyimide precursor                                                (polyamide acid)                                                              Isopropyl alcohol      50       ml                                            Ethanol                50       ml                                            ______________________________________                                    

The thus coated glass substrate was further heated at 230° C. for 1 hourto cause a dehydration-ring closure reaction, thereby to convert thecoating film into a polyimide film.

The polyimide film on the glass substrate was then rubbed in onedirection under the pressure of 100 g/cm². A pair of the thusrubbing-treated plastic substrate were superposed each other so thattheir rubbing directions were in parallel with each other and secured toeach other with a gap of 1 μ therebetween by sealing the peripheryexcept for a port for liquid crystal injection, whereby a blank cell wasprepared.

Separately, a liquid crystal composition was prepared by mixing 4 partsby weight of 4-cyanobenzylidene-4'-(2-methylbutyl)aniline with 100 partsby weight of 4-octyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port and into the above-provided cellunder vacuum, and the injection port was sealed. The liquid crystal cellthus formed was gradually cooled at a rate of 0.5° C./hr and wasobserved through a microscope while being sandwiched between a pair ofpolarizers arranged in the cross nicol relationship, whereby amonodomain of SmC* phase with non-spiral structure was found to beformed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 800 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as a comparative experiment, a liquid crystal devicewas prepared in the same manner as described above except that the4-cyanobenzylidene-4'-(2-methylbutyl)aniline was omitted. The liquidcrystal device was subjected to similar microscopic observation. As aresult, a monodomain of SmC* phase with non-spiral structure was foundto be formed at the initial stage whereas the monodomain of SmC* phasewas not retained after the 800 hours of durability test.

EXAMPLE 12

A blank cell as used in Example 1 was provided.

Separately, a liquid crystal composition was prepared by mixing 5 partsby weight of cholesteric nonanate with 100 parts by weight of4-(2'-methylbutyl)-phenyl-4'-octyloxybiphenyl-4-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port of the above-provided cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phase withnon-spiral structure was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 500 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as a comparative experiment, a liquid crystal devicewas prepared in the same manner as described above except that thecholesteryl nonanate was omitted. The liquid crystal device wassubjected to similar microscopic observation. As a result, a monodomainof SmC* phase with non-spiral structure was found to be formed at theinitial stage whereas the monodomain of SmC* phase was not retainedafter the 500 hours of durability test.

EXAMPLE 13

A blank cell as used in Example 2 was provided.

Separately, a liquid crystal composition was prepared by mixing 10 partsby weight of 4-(2-methylbutyl)phenyl-4'-decyloxybenzoate with4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port and into the above-provided cell,and the injection port was sealed. The liquid crystal cell thus formedwas gradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship whereby a monodomain of SmC* phase withnon-spiral structure was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 700 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as a comparative experiment, a liquid crystal devicewas prepared in the same manner as described above except that the4-(2-methylbutyl)-phenyl-4'-decyloxybenzoate was omitted. The liquidcrystal device was subjected to similar microscopic observation. As aresult, a monodomain of SmC* phase with non-spiral structure was foundto be formed at the initial stage whereas the monodomain of SmC* phasewas not retained after the 700 hours of durability test.

EXAMPLES 14 AND 15

Liquid crystal devices were prepared in the same manner as in Example 13except that the4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate was replacedby 4-pentylphenyl-4-(4'-methylhexyl)phenyl-4'-carboxylate (Example 14),and p-n-octyloxybenzoic acid-p'-(2-methylbutyloxy)phenyl ester (Example15), respectively. The liquid crystal devices were subjected to similarmicroscopic observation whereby a monodomain of SmC* with non-spiralstructure was respectively found to be formed and observed to beretained after the 700 hours of the durability test as carried out inExample 13.

EXAMPLES 16-18

Liquid crystal devices were prepared in the same manner as in Example 13except that the 4-(2-methylbutyl)phenyl-4'-decyloxybenzoate was replacedby 4-(2"-methylbutyl)-4'-cyanobiphenyl (Example 16), cholesterylbenzoate (Example 17) and 4-(2'-methylbutyloxy)-4'-cyanobiphenyl(Example 18), respectively. The liquid crystal devices were subjected tosimilar microscopic observation whereby a monodomain of SmC* withnon-spiral structure was respectively found to be formed and observed tobe retained after the 700 hours of the durability test as carried out inExample 13.

EXAMPLE 19

A blank cell as used in Example 10 was provided.

Separately, a liquid crystal composition was prepared by mixing 4 partsby weight of 4-(2-methylbutyl)-4'-hexyloxyazobenzene with 100 parts byweight 4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port of the above-provided cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phase withnon-spiral structure was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 500 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as a comparative experiment, a liquid crystal devicewas prepared in the same manner as described above except that the4-(2-methylbutyl)-4'-hexyloxyazobenzene was omitted. The liquid crystaldevice was subjected to similar microscopic observation. As a result, amonodomain of SmC* phase with non-spiral structure was found to beformed at the initial stage whereas the monodomain of SmC* phase was notretained after the 500 hours of durability test.

EXAMPLES 20-22

Liquid crystal devices were prepared in the same manner as in Example 19except that the 4-(2-methylbutyl)-4'-hexyloxyazobenzene was replaced y4-(2"-methylbutyl)-4'-cyanobiphenyl (Example 20). cholesteryl benzoate(Example 21) and 4-(2"-methylbutyloxy)-4'-cyanobiphenyl (Example 22),respectively. The liquid crystal devices were subjected to similarmicroscopic observation whereby a monodomain of SmC* with non-spiralstructure was respectively found to be formed and observed to beretained after the 500 hours of the durability test as carried out inExample 19.

EXAMPLE 23

A blank cell as used in Example 1 was provided.

Separately, a liquid crystal composition was prepared by mixing 75 partsby weight of 4-hexyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-carboxylatewith 100 parts by weight of4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port of the above-provided cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phase withnon-spiral structure was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 700 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as comparative experiments, liquid crystal deviceswere prepared in the same manner as described above except that the twoliquid crystals used in the above liquid crystal device were separatelyused. The liquid crystal devices were subjected to similar microscopicobservation. As a result, in each case, a monodomain of SmC* phase withnon-spiral structure was found to be formed at the initial stage whereasthe monodomain of SmC* phase was not retained after the 700 hours ofdurability test.

Further, when 20 parts by weight of DOBAMBC was added to 100 parts byweight of the above-mentioned liquid crystal composition to obtain aliquid crystal composition. The thus obtained liquid crystal compositionwas used to prepare a liquid crystal device in the same manner. Theliquid crystal device was subjected to similar microscopic observation,whereby a monodomain of SmC* phase with non-spiral structure was foundto be formed and observed to be retained after the durability test for aprolonged time which was 1000 hours longer than that in theabove-mentioned example.

EXAMPLE 24

A blank cell as used in Example 2 was provided.

Separately, a liquid crystal composition was prepared by mixing 70 partsby weight of4-(octyloxyphenyl)-4-(2"-methylbutyl)biphenyl-4'-carboxylate with 100parts by weight of4-pentylphenyl-4-(4"-methylhexyl)biphenyl-4'-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port and into the above-provided cell,and the injection port was sealed. The liquid crystal cell thus formedwas gradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phase withnon-spiral structure was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 700 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as comparative experiments, liquid crystal deviceswere prepared in the same manner as described above except that the twoliquid crystals used in the above liquid crystal device were separatelyused. The liquid crystal devices were subjected to similar microscopicobservation. As a result, in each case, a monodomain of SmC* phase withnon-spiral structure was found to be formed at the initial stage,whereas the monodomain of SmC* phase was not retained after the 700hours of durability test.

Further, when 20 parts by weight of DOBAMBC was added to 100 parts byweight of the above-mentioned liquid crystal composition to obtain aliquid crystal composition. The thus obtained a liquid crystalcomposition was used to prepare a liquid crystal device in the samemanner. The liquid crystal device was subjected to similar microscopicobservation whereby a monodomain of SmC* phase with non-spiral structurewas found to be formed and observed to be retained after the durabilitytest for a prolonged time which was 1000 hours longer than that in theabove-mentioned example.

EXAMPLES 25 AND 26

Liquid crystal devices were prepared in the same manner as in Example 23except that the4-(2-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate was replacedby 4-pentylphenyl-4-(4"-methylhexyl)biphenyl-4'-carboxylate (Example25), and p-n-octyloxybenzoic acid-p'-(2-methylbutyloxy)phenyl-ester(Example 26). The liquid crystal devices were subjected to similarmicroscopic observation whereby a monodomain of SmC* phase withnon-spiral structure was respectively found to be formed and observed tobe retained after the 700 hours of the durability test as carried out inExample 23.

Further, two liquid crystal devices respectively containingthree-component liquid crystal compositions were prepared in the samemanner as explained in Example 23 except that HOBACPC was used in placeof DOBAMBC. The liquid crystal devices were subjected to similarmicroscopic observation, whereby a monodomain of SmC* with non-spiralstructure was observed to be formed at the initial stage and retainedafter the durability for 1700 hours for each device.

EXAMPLE 27

A blank cell as used in Example 10 was provided.

Separately, a liquid crystal composition was prepared by mixing 80 partsby weight of 4-hexyloxyphenyl-4-(2"-methylbutyl)biphenyl-4'-carboxylatewith 100 parts by weight of4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate.

The liquid crystal composition was heated into the isotropic phase andinjected through the injection port of the above-provided cell, and theinjection port was sealed. The liquid crystal cell thus formed wasgradually cooled at a rate of 0.5° C./hr and was observed through amicroscope while being sandwiched between a pair of polarizers arrangedin the cross nicol relationship, whereby a monodomain of SmC* phase withnon-spiral structure was found to be formed.

The device containing the liquid crystal composition in the SmC* phasewas held under the condition for 500 hours and then subjected to similarmicroscopic observation, whereby the SmC* phase with non-spiralstructure was found to be retained.

On the other hand, as comparative experiments, liquid crystal deviceswere prepared in the same manner as described above except that the twoliquid crystals used in the above liquid crystal device were separatelyused. The liquid crystal devices were subjected to similar microscopicobservation. As a result, in each case, a monodomain of SmC* phase withnon-spiral structure was found to be formed at the initial stage,whereas the monodomain of SmC* phase was not retained after the 500hours of durability test.

Further, when 20 parts by weight of OOBAMBCC was added to 100 parts byweight of the above-mentioned liquid crystal composition to obtain aliquid crystal composition. The thus obtained a liquid crystalcomposition was used to prepare a liquid crystal device in the samemanner. The liquid crystal device was subjected to similar microscopicobservation whereby a monodomain of SmC* phase with non-spiral structurewas found to be formed at the initial stage and observed to be retainedafter the durability test for a prolonged time which was 800 hourslonger than that in the above-mentioned example.

EXAMPLES 28 AND 29

Liquid crystal devices were prepared in the same manner as in Example 27except that the4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate was replacedby 4-pentylphenyl-4-(4"-methylhexyl)biphenyl-4'-carboxylate (Example 28)and p-n-octyloxybenzoic acid-p'-(2-methylbutyloxy)phenyl ester.

The liquid crystal devices were subjected to similar microscopicobservation whereby a monodomain of SmC* phase with non-spiral structurewas respectively found to be formed and observed to be retained afterthe 700 hours of the durability test as carried out in Example 24.

Further, two liquid crystal devices respectively containingthree-component liquid crystal compositions were prepared in the samemanner as explained in Example 23 except that DOBAMBC was used in placeof OOBAMBCC. The liquid crystal devices were subjected to similarmicroscopic observation, whereby a monodomain of SmC* with non-spiralstructure was observed to be formed at the initial stage and retainedafter the durability for 2000 hours for each device.

EXAMPLES 30 AND 31

Liquid crystal devices were prepared in the same manner as in Example 24except that the 4-pentylphenyl-4-(4"-methylhexyl)biphenyl-4'-carboxylateused in Example 24 was replaced by4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate (Example 30)and p-n-octyloxybenzoic acid-p'-(2-methylbutyloxy)phenyl ester. Theliquid crystal devices were subjected to similar microscopic observationwhereby a monodomain of SmC* phase with non-spiral structure wasrespectively found to be formed and observed to be retained after the700 hours of the durability test as carried out in Example 24.

Further, two liquid crystal devices respectively containingthree-component liquid crystal compositions were prepared in the samemanner as explained in Example 23 except that MBRA 8 was used in Placeof DOBAMBC. The liquid crystal devices were subjected to similarmicroscopic observation, whereby a monodomain of SmC* with non-spiralstructure was observed to be formed at the initial stage and retainedafter the durability for 1500 hours for each device.

The liquid crystal devices produced in the above examples were drivenfor wiring with voltage signals having waveforms as shown in FIG. 8(driving voltage 30 V, pulse width 500 msec), whereby the written imageswere memorized without inversion for a duration of one frame.

What is claimed is:
 1. A liquid crystal device, comprising: (a) a pairof base plates each having an orientation control film thereon, and (b)a liquid crystal composition interposed between the base plates; saidliquid crystal composition comprising a mixture including at least oneliquid crystal compound which has a temperature range in which it showschiral smectic phase and at least one optically active substance whichdoes not have a temperature range in which it shows chiral smecticphase; said liquid crystal composition having a temperature range inwhich it shows cholesteric phase and being placed in chiral smecticphase which has been formed through cholesteric phase on temperaturedecrease; said liquid crystal composition comprising liquid crystalmolecules having long axes forming a pre-tilt in the chiral smecticphase.
 2. A liquid crystal device according to claim 1, wherein saidliquid crystal composition is placed in chiral smectic phase which hasbeen formed through successive phase transition from isotropic phase,then cholesteric phase, then smectic A phase and to the chiral smecticphase on temperature decrease.